1. Field of the Invention
The present invention relates to an improved process for recovering condensable compounds from inert gas-condensable compound vapor mixtures.
2. Description of the Prior Art
In the storage and transfer of liquids formed from condensable compounds, portions of the liquids often vaporize and mix with air or other gas in contact therewith. Such mixtures generally can not be vented directly to the atmosphere due to the resulting pollution of the environment or the creation of a fire or explosion hazard. The vaporized compounds, referred to herein as "condensable compounds" can be produced from multi-compound hydrocarbon liquids such as gasoline and kerosene, single compound hydrocarbon liquids such as benzene and methanol and non-hydrocarbon compounds such as carbon tetrachloride and the like.
A variety of processes have heretofore been developed and used for removing condensable compound vapors from inert gas-condensable compound vapor mixtures whereby the remaining inert gas, e.g., air or nitrogen, can be safely vented to the atmosphere. The removed condensable compounds are generally liquified and recombined with the liquid from which they were vaporized thereby making their recovery economically advantageous.
A commercially successful process and apparatus which has been utilized for recovering both hydrocarbon and non-hydrocarbon condensable compounds from air-condensable compound vapor mixtures is described in U.S. Pat. No. 4,276,058 issued Jun. 30, 1981. In accordance with that process, the air-condensable compound mixture is caused to flow through a bed of solid adsorbent having an affinity for the condensable compounds. As the mixture passes through the bed, a major portion of the condensable compounds contained in the mixture are adsorbed on the bed, and a residue gas stream is produced which is substantially free of condensable compounds and as a result can be vented to the atmosphere. While a first bed of the solid adsorbent is adsorbing condensable compounds from the vapor mixture, a second bed of solid adsorbent having condensable compounds adsorbed thereon is regenerated by evacuation. The evacuation is accomplished by vacuum pumping using a liquid seal vacuum pump in combination with the introduction of a small quantity of heated condensable compound-free air into the solid adsorbent so that additional adsorbed compounds are stripped therefrom. The air-condensable compound vapor mixture produced in the regeneration of the solid adsorbent is contacted with a liquid absorbent so that a major portion of the condensable compounds are absorbed therefrom and recovered.
While various liquids have been utilized in liquid seal vacuum pumps utilized for evacuating beds of solid adsorbent such as oil, water and ethylene glycol solutions, problems have been and are presently experienced as a result of the condensable compounds removed from the solid adsorbent intimately contacting the pump seal liquid. The intimate contact between the condensable compounds and the seal liquid leads to difficulty in separating the recovered condensable compound product from the seal liquid which can in turn cause unexceptable losses of seal liquid, contamination of the recovered condensable compound product or both.
The use of liquid seal vacuum pumps in processes and apparatus of the type described above is highly advantageous in that such pumps are relatively inexpensive, efficient and safe. However, when the condensable compounds to be recovered are completely or partially soluble in the vacuum pump seal liquids that can be used, a process including the use of a liquid seal vacuum pump often can not be utilized. Thus, there is a need for an improved process for recovering condensable compounds from inert gas-condensable compound vapor mixtures which utilizes a liquid seal vacuum pump, but overcomes the problems mentioned above.